Ocular lens composition and method of formation

ABSTRACT

A gas permeable (GP) ocular lens composition and method of formation are disclosed wherein 98-70% by wgt. of a first polymer component, selected for desired characteristics including gas permeability, and 2-30% by wgt. of a second polymer component, selected for basic GP lens characteristics such as rigidity, structural stability and desired refractive index, are combined in an interpenetrating polymer network (IPN) structure forming a thermoplastic composition having optical clarity/compatibility and facilitating low cost formation by molding or thermoforming. The first polymer component is a block co-polymer from first and second monomers. The resulting lens composition has a flexure modulus in the range of about 2,000-50,000 psi; preferably about 5,000-40,000 psi; and more preferably about 20,000-40,000 psi. In one embodiment, the lens comprises a central portion and an annular portion of different characteristics. In another cosmetic embodiment, a film with an image of an iris is encapsulated in the composition.

This application is a division of application Ser. No. 08/255,570, filedJun. 13, 1994, now U.S. Pat. No. 5,723,541, which is acontinuation-in-part of application Ser. No. 08/077,857, filed Jun. 16,1993, now abandoned.

FIELD OF THE INVENTION

The present invention relates to ocular lenses and their manufactureand, more particularly, to the composition and manufacture of suchproducts commonly characterized as gas permeable (GP) ocular lenses.

BACKGROUND OF THE INVENTION

This is a continuation-in-part of U.S. patent application Ser. No.08/077,857 filed Jun. 16, 1993 under assignment to the assignee of thepresent invention, now abandoned.

Lenses of the type contemplated by the present invention are generallycharacterized as ocular lenses and encompass lenses intended for directcontact with the eye (including both corneal and scleral type lenses).In addition, the term "contact lens" as employed herein is intended toinclude not only conventional contact lenses which are generallyarranged on the surface of the eye but also intraocular or insert-typelenses commonly employed as surgical implants.

The term "contact lens" includes both scleral type lenses as well asmore conventional lenses commonly referred to as contact lenses. In thisregard, scleral type lenses generally have an outer annular portion ofthe lens adapted for contact with the eye. A pocket or recess is formedbetween the eye and a central portion of the lens and can be filledeither with ophthalmological solution or tear solution fluid. The moreconventional contact type lens referred to above, by contrast, is ingenerally uniform contact with the eye except for a thin film of tearfluid or the like. It is also to be understood that the term "contactlens" includes other varieties of lenses such as soft lenses, hardlenses, etc.

Hard ocular lenses, such as contact lenses, were initially madeexclusively from glass. As interest and experience increased in polymertechnology, glass was replaced by poly(methyl methacrylate) which thenbecame the standard composition for such lenses because of itstoughness, optical properties and physiological inactivity, as well asrelative ease of manufacture (as least compared to prior art at thetime), for example by turning on a suitable lathe.

Although hard contact lenses formed either from glass or poly(methyl.methacrylate) could be fabricated in a full range of opticalcorrections, both materials were essentially impermeable to oxygen andtherefore, as further explained below, could not be worn by a user forextended periods. Rather, the initial hard contact lenses were limitedgenerally to daily usage. Although the hard contact lenses were alsoreadily capable of sterilization, for example during overnight non-use,interest rapidly developed in contact lenses which could be worn forextended periods of time and which were inherently more comfortable.

This interest led to the development of so-called "soft contact lenses"which emerged with the development of a class of polymers generallyreferred to as "hydrogels". The key to the development of soft contactlenses was their relatively high water content yielding a soft flexiblematerial with oxygen transport taking place through the body of the lenslargely by means of the water component rather than the lens polymeritself. For this reason, so-called soft contact lenses were capable ofextended wear, were immediately more comfortable and became highlypopular.

However, soft contact lenses have tended to exhibit certain undesirablecharacteristics even though they usually present adequate oxygenpermeability to avoid damage to the cornea over extended periods ofwear. Such disadvantages include the inability to fabricate soft contactlenses to correct for all types of visual defects or to provide the fullrange of optical correction required for all users. Additionally,dehydration causes visual acuity to decrease during the days wearingperiod. Furthermore, soft contact lenses are generally characterized asbeing fragile and having a relatively short use life. Finally, softcontact lenses have been associated with infection of the eye frommicroorganisms and, therefore require a stringent sterilization andmaintenance regimen.

The term "extended" use or wear may have various meanings in connectionwith contact lenses. Generally, although that term may refer to use orwear over a long term of, for example, thirty days, the term is usedherein to signify use or wear at least overnight.

Even more recently, interest has developed in "rigid gas permeable"contact lenses or RGP contact lenses which combine the desirablefeatures of hard contact lenses as noted above and the permeability andextended wear possibilities of soft contact lenses. Permeability isconsidered a fundamental requirement, particularly for RGP contactlenses, in order to permit the transport of atmospheric oxygen throughthe lens to the cornea. This is necessary because, unlike most tissuesin the body, the human cornea lacks blood vessels for supplying oxygento the cornea in the form of oxygenated blood. Rather, the corneanormally obtains oxygen directly from surrounding air. Contact lensesnaturally interfere with this oxygen source, producing the need for gaspermeability as noted above to avoid damage to the cornea, particularlyduring extended wear.

RGP contact lenses may be considered to have three essentialrequirements because of their function as an extension of the cornea.Initially, it is necessary as noted above to maintain a continuousundisturbed supply of oxygen to the cornea. As noted above, this istypically achieved by maintaining gas permeability in the contact lensitself. Secondly, it is necessary for the lens to be structurally stableat least to the extent of resisting deforming forces of the eyelidduring blinking, for example in order to avoid visual instability.Thirdly, the composition of the lens must provide surface wettabilitysufficient in order to enable a continuous tear film to be maintainedbetween the lens and the cornea. At the same time, desirable surfacecharacteristics include compatibility with the eye and the ability toavoid or minimize accumulation of proteinaceous material on the surfaceof the lens. Still other characteristics are also important, includingcomfort, coloration, and clarity. Finally, the material of an RGP ocularlens should be inexpensive to process into a completed lens. Thischaracteristic is particularly important for low-cost lenses such asdisposable lenses, which are becoming of greater interest.

The RGP contact lenses developed to date have been found satisfactoryfor certain of the above requirements with the possible exception ofcost, comfort and, in some cases, wettability and structural stability.With available polymer technology, RGP lenses can incorporate relativelyhigh oxygen permeability. At the same time, the RGP lenses can befabricated in a broad range of optical corrections with the ability tocorrect most visual defects.

However, fabrication techniques for RGP contact lenses to date arerelatively expensive, requiring techniques such as substantial machiningon special lathes. It has further been found that contact lensesproduced by these techniques tend to exhibit "creep", leading to changesin curvature of the lenses and compromising their structural stability.Additionally, some RGPs present comfort problems because of the lack ofadequate wettability of some polymers and the inherent highly-rigid ornon-flexible nature of the lens.

Generally, a broad range of polymers and combination of polymers andtechniques have been considered to date in the development of desirablecontact lenses. For example, a series of patents, as noted below, havedisclosed a variety of linear co-polymers including acrylates forachieving desirable characteristics in RGP contact lenses.

Initially, Gaylord U.S. Pat. No. 3,808,179 issued Apr. 30, 1974 underassignment to Polycon Laboratories, Inc. disclosed contact lensesfabricated from a co-polymer of a fluoroalkyl acrylic ester and an alkylacrylate or methacrylate to exhibit increased oxygen permeability. Awide variety of fluoroalkyl acrylic esters was disclosed in that patent.

Gaylord U.S. Pat. No. 4,120,570 issued Oct. 17, 1978 under assignment toSyntex (U.S.A.), Inc. disclosed yet another class of contact lensmaterials including in large part a polysiloxanylalkyl ester of aspecified structure and allegedly having various improved functions suchas improved oxygen permeability and surface wettability.

Gaylord Reissue Pat. No. 31,406 reissued Oct. 4, 1983 under assignmentto Syntex (U.S.A.), Inc. further disclosed contact lenses fabricatedfrom a co-polymer of a polysiloxanylalkyl acrylic ester (see the abovepatent) and an alkyl acrylic ester for the specified purpose ofincreased oxygen permeability. Another class of materials considered incontact lenses are silicone elastomers, the simplest of which may becharacterized as poly(dimethylsiloxanes). A wide variety of suchmaterials and reference to their possible use in contact lenses is notedin an article by Barry Arkles, "Look What You Can Make Out ofSilicones", a reprint from CHEMTECH, 1983, 13, pp. 542-555 and ArklesU.S. Pat. Nos. 4,478,981 issued Oct. 23, 1984 and 4,550,139 issued Oct.28, 1985.

Similarly, Laurin U.S. Pat. No. 3,994,988 issued Nov. 30, 1976 underassignment to Baxter Travenol Laboratories, Inc. disclosed co-polymersof polysiloxane, polycarbonate and polyester constituents particularlycontemplated for a wide variety of medical applications includingcontact lenses.

Of related interest, a survey of various co-polymer systems was setforth in a book by Noshay and McGrath, Block Co-Polymers, Overview andCritical Survey, Academic Press, New York (1977), pp. 393, 394, et al.This reference is particularly noted in connection with the presentinvention in that it defines block co-polymers and sets forth numerouscombinations of polymers which may be combined in block co-polymersuseful for ocular lens compositions.

Additional block co-polymers particularly contemplated for use incontact or ocular lenses as defined by the present invention weredisclosed in German Patent Application 2324654 filed May 19, 1973 underassignment to Biocontacts, Inc. from Stark, Auslander, Mandell and Marg.A corresponding disclosure appeared in French Application 2.185.653,Registration No. 73.181.11, also assigned to Biocontacts, Inc. from thesame inventors. Both of these patents relied for priority on U.S. patentapplication Ser. No. 255,220, filed May 19, 1972 and subsequentlyabandoned. The above noted patents disclosed various block co-polymersof silicone and polycarbonate for forming contact lenses. Generally, thematerials disclosed in these patents were not sufficiently stiff topermit machining.

Particularly in connection with the references noted immediately above,it is important to distinguish between block co-polymers and otherco-polymers which are commonly referred to as linear or randomco-polymers. Generally, as their name implies, block co-polymers arecharacterized by blocks or continuous chains of specific chemicalspecies tending to demonstrate unique properties of the respectivepolymeric species.

By contrast, random co-polymers tend to be relatively short chain units,often with single monomer units in varying distribution along the chainlink. In any event, the random co-polymers do not include clearlydefined blocks of selected polymers as in block co-polymers.

Distinctions between block co-polymers and other co-polymers of the typereferred to above are also set forth within a reference by Sperlingnoted and discussed in greater detail below.

Lim, et al, U.S. Pat. No. 4,536,554 issued Aug. 20, 1985 underassignment to Barnes-Hind, Inc. disclosed various compositions ofhydrophilic polymers and contact lenses formed from those polymers, theLim, et al. patent further disclosing transparent, optically clearinterpenetrating network polymers for forming products such as contactlenses from such polymer systems. The interpenetrating polymer network(IPN) was specifically employed for combining two polymers in networkform with one of the polymers being bound by the other polymer andallowed to swell to take on a substantial water content as high as 65%by weight. In any event, the IPN system of the Lin, et al. patent wasspecifically directed toward standard water-based soft hydrogel contactlenses.

The preceding references are believed to be fairly representative of theprior art. Furthermore, it is emphasized that although certain polymersystems have been developed lending themselves to specific applicationsin contact lenses, there remains a great need for a further improvedcontact lens, particularly a contact lens having a combination of manyof the desirable properties; i.e., comfort, structural stability, highgas permeability, wettability, and clarity, while also having theability to be manufactured in a simple, inexpensive manner, for exampleby molding, in order to particularly make the lenses available forrelatively low-cost applications, such as for disposable use.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved gaspermeable (GP) contact lens composition and method of forming thecontact lens to achieve the above-stated desirable qualities.

It is a further object of the invention to provide GP ocular lenscompositions and a method of formation wherein the compositions includea first polymer component and a second polymer component, the first andsecond polymer components being combined in an interpenetrating polymernetwork (IPN) to form the GP ocular lens composition, the first polymercomponent being selected to provide gas permeability and preferablyother desirable properties as well, the second polymer componentproviding characteristics including flexibility or rigidity as desired,structural stability and desired refractive index, the first and secondpolymer components also being selected in combination for forming athermoplastic composition having optical clarity and compatibility andfacilitating low cost formation of the GP ocular lens by techniquescommonly referred to as molding or thermoforming.

It is another object of the invention to provide an improved gaspermeable contact lens composition and method of forming such a contactlens having a novel combination of features including flexibility,moldability and gas permeability particularly suitable for extendedwear.

It is even more preferably contemplated that contact lenses according tothe present invention have a particularly desirable combination of gaspermeability and lens rigidity as discussed in greater detail below.

The second polymer component is preferably selected from a class ofpolymers which exhibit the basic lens characteristics referred to aboveand selected from the class consisting of acrylates (includingmethacrylates, diacrylates and dimethacrylates), pyrolidones, styrenes,amides, acrylamides, carbonates, vinyls, acrylonitriles, nitrites,sulfones, siloxanes, glycols, ethers and combinations of the above.

Furthermore, the second polymer component is preferably aninterpenetrating network component forming an interpenetrating networkwith respect to the first polymer component in the ocular lenscomposition.

It is also an object of the invention to provide such a gas permeablecontact lens composition and method of forming the lens wherein theinterpenetrating network is formed by solution polymerization. Morepreferably, the interpenetrating network of the lens composition isformed by solution polymerization with a relatively high concentrationof a free radical initiator of greater than 0.9 molar percent ofmonomer, preferably at least about 1.0 molar percent of monomer and morepreferably at least about 1.2 molar percent of monomer.

It is a still further object of the invention to provide ocular lenscompositions and a method of formation wherein the first polymercomponent is selected for producing desirable characteristics inaddition to high gas permeability in the lens, the additional desirablecharacteristics being selected from the class consisting of comfort asdetermined by flexibility or rigidity, wettability, bio-compatibility,soil resistance, and dimensional stability.

Even more preferably, the first polymer component is a block co-polymerformed from first and second monomers. The first and second monomers arepreferably selected for providing or enhancing different characteristicsin the ocular lens composition as noted above. In specific examples setforth below, the first and second monomers of the first polymercomponent may be combinations selected from the classes consisting ofsilicones and polycarbonates.

The ratio of the first and second polymer component within the GP ocularlens composition is critical to the invention. Generally, the inventioncontemplates a relatively small proportion of the second polymercomponent added to a relatively large proportion of the block copolymerforming the first polymer component in order to impart specificproperties considered important to an improved contact lens according tothe present invention.

More specifically, since the silicone component of the block copolymercontributes high oxygen permeability to the lens and contributes comfortdue to its flexible nature, it is an objective of this invention toprovide significantly high levels of the oxygenpermeability/comfort-flexibility contributing components.

It is a still further related object of the invention to provide ocularlens compositions and a method of formation wherein the second polymercomponent is selected for varying one or more characteristics of theocular lens composition as listed above in order to meet therequirements of different ocular lens applications.

Within the various embodiments of the invention as summarized above,certain components such as the first and second polymer components andthe first and second monomers may be selected from references such asthose noted above. However, the present invention further requires thecombination of those components to achieve the specified characteristicsas noted above and to form an interpenetrating polymer network (IPN),preferably with the second polymer component as a thermoplastic IPNcomponent with respect to the first polymer component. Thisthermoplastic IPN does not depend upon crosslinking to achievecompatibility among the components. Compatibility is essential toachieving the transparency required by a contact lens. Achievingcompatibility through crosslinking will, a priori, diminish thepermeability desired for an extended wear contact lens.

It is again emphasized that the thermoplastic IPN structure referred toabove is essential within the ocular lens compositions of the presentinvention. In that regard, an understanding of the combined materials inthe ocular lens compositions of the present invention is believed to bebest provided by nomenclature developed by L. H. Sperling in his text,Interpenetrating Polymer Networks and Related Materials, Plenum Press,New York, N.Y. (1981). This text is accordingly incorporated herein,particularly Chapter 3 which specifically deals with nomenclature asreferred to above. In general, the Sperling nomenclature is technicallyvalid and has been proposed as a standard approach to naming complexpolymer mixtures. The Sperling nomenclature is also particularly usefulin connection with the present invention in order to distinguish theinterpenetrating network structure of the invention over various priorart references.

The Sperling nomenclature answers three questions about the chemicalentity of the IPN which are not answered by conventional chemicalnomenclature. These three features include: (1) the identities of thepolymers being combined; (2) the principal modes of combination; and (3)the time sequence or addition sequence of the reaction or reactionsforming the entity.

For example, at least one of the examples of the present invention asdescribed below includes a thermoplastic block co-polymer which isprepared first. The block co-polymer subsequently becomes part of an IPNthrough the addition of one or more monomers. This is an example of asequential IPN because the block co-polymer is formed first and theadditional polymer is subsequently created within the structure of theblock co-polymer, in solution.

The combination of the two components or monomers in the blockco-polymer is indicated by the link "b" and the subsequent reaction offurther monomers to form the IPN is indicated by the link "i".Thereafter, if P1 and P2 indicate the polymeric chains of a blockco-polymer and P3 represents a polymer later created in the presence ofthe block co-polymer to form an IPN, then the general form of thecombination or composition of the present invention may be shown as:

    (P1--b--P2)--i--P3.

This is accordingly a broad statement of the thermoplastic IPN structurefor the present invention, at least where the first polymer component isa block co-polymer. The sequence of formation or combination of theelements of the IPN is represented by the left-to-right orientation ofthe name.

As a further example, the IPN described below in Example 1 may thereforebe described as: poly(dimethylsiloxane)-b-poly(carbonate)!-i-poly(methylmethacrylate) or, the IPN structure may be abbreviated as follows:

     PDMS--b--PC!--i--PMMA;

wherein, according to widely-accepted abbreviations, PDMS signifiespoly(dimethylsiloxane); PC signifies bisphenol A poly(carbonate); andPMMA signifies poly(methyl methacrylate).

It will be apparent from the following description that otherinterpenetrating polymer network structures defined in accordance withthe present invention may be represented in similar fashion by theSperling nomenclature set forth above.

By contrast, to further define the ocular lens compositions of thepresent invention, the interpenetrating polymer network structure orportions thereof may also be represented by conventional chemicalnomenclature which, however, as noted above, does not indicate the orderof formation or combination for various components. For example, theblock co-polymer of Example 1 as referred to above and discussed ingreater detail below, may be identified by the chemical nomenclature##STR1##

In the above structure, a first monomer component is indicated inbrackets with the subscript n indicating the number of repeating unitsof that monomer. Similarly, a second monomer is also indicated inbrackets with the subscript m indicating the number of repeating unitsfor the second monomer. In a typical formulation, n may equalapproximately 20, for example, and m may vary, for example, from about3.5 to about 70.

More broadly, the block co-polymer may be represented by thenomenclature X_(n) rY_(m), where X represents a first monomer or monomercomponent, Y represents a second monomer or monomer component, and r isa linking substituent. The subscripts n and m are as defined above. Itwill be apparent that a broad range of block co-polymers can besignified by this structure.

It is again noted that block co-polymers as represented above aredisclosed by various references such as the Noshay article referred toabove. Block co-polymers are basically different from random orcollinear polymers as disclosed in certain of the other referencesabove. More specifically, the block co-polymers are formed withidentifiable repeating sequences providing predictable characteristicsof specific polymers unlike the random or alternating distribution oflinear co-polymers as discussed above.

Additional features are either contemplated by the present invention orare possible in combination with the composition of the invention.

Additional modifications and variations in the present invention will beapparent from the following description having reference to theaccompanying drawing and also with specific reference to the individualexamples set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow sheet broadly illustrating steps for forming a gaspermeable contact lens composition according to the present invention.

FIG. 2 is a flow sheet generally similar to that of FIG. 1 but specificto a preferred embodiment of the invention.

FIG. 3 is a graphical representation of oxygen permeability for arelatively wide range of compositions described in Example 1.

FIG. 4 is a plan view of a contact lens formed in accordance withExample 10.

FIG. 5 is an axially sectioned view of the lens of FIG. 4.

FIG. 6 is a view of a contact lens formed in accordance with Example 11.

FIG. 7 is an axially sectioned view of the contact lens of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As noted above, the invention relates to an ocular lens composition andmethod of preparation wherein first and second polymer components arecombined in an interpenetrating polymer network to form the gaspermeable ocular lens composition, the second polymer componentpreferably providing an interpenetrating network with respect to thefirst polymer component.

As further noted above, the first and second polymer components arerespectively selected for providing selected characteristics within theGP ocular lens composition. Preferably, the second polymer component isselected for providing basic GP lens characteristics includingstructural stability, wettability, desired refractive index as necessaryin any lens composition, and the ability to additionally tailorflexibility or rigidity as desired. At the same time,the first polymercomponent is selected for providing additional desired characteristicsin the GP lens composition, particularly characteristics adapting thecontact lens for extended or long term use. For that reason, the firstpolymer component is preferably selected for providing necessarycharacteristics such as high gas permeability and flexibility orrigidity as desired for comfort, and also additional desirablecharacteristics selected, for example, from the class of characteristicsconsisting of structural stability, thermoplasticity, wettability, usercompatibility, and soil resistance.

As noted above, the first and second polymer components may thus beselected from references such as those noted above which disclosevarious polymers and characteristics which they tend to develop incontact lens compositions. As a specific example, a number of thereferences disclose the use of methacrylates as a basic componentforming rigidity and structural stability in the lenses. To the extentthat the references are of assistance in understanding or broadening thescope of the present invention, they are incorporated herein byreference.

However, the present invention further requires selection of the firstand second polymer components in combination for forming a thermoplasticcomposition having optical clarity and compatibility and facilitatinglow cost formation of the ocular lens by techniques commonly referred toas molding or thermoforming.

Within the invention as summarized above, the desirable characteristicof thermoplasticity is preferably produced by the first polymercomponent. For that purpose, the first polymer component may include,for example, polymers such as polycarbonates, polysulfone andpolystyrene. Additional polymers suitable for producing thermoplasticityin the ocular lens composition are disclosed, for example, by the Noshayreference which is also incorporated herein by reference for thatpurpose.

More preferably, the first polymer component is formed as a blockco-polymer from first and second monomers which, in turn, are selectedfor achieving different characteristics in the finished GP ocular lenscomposition. In this manner, even greater versatility is achieved forthe GP ocular lens of the invention.

As one example, the first monomer may be selected for primarilyachieving the desired characteristic of oxygen permeability in the GPocular lens composition and may include polymers such as silicones,fluorine polymers and dimethyl pentene, as well as possibly otherpolymers for that purpose.

At the same time, the second monomer may be selected, for example, toachieve desired thermoplasticity in the final GP contact lenscomposition and may include one or more of the resins noted above.

The first and second monomers may be combined into a block co-polymeraccording to various known techniques with the block co-polymer formingthe first polymer component of the invention.

The use of the first and second polymer components within aninterpenetrating polymer network as noted above provides additionaladvantages in GP ocular lenses including the ability to vary basiccharacteristics such as rigidity or hardness (within a suitable rangefor GP lenses) and gas permeability. For example, rigidity may beadjusted by selecting different types of polymers for the second polymercomponent while permeability may probably be most readily varied byselecting the appropriate polymer either in the first polymer componentor in the first monomer of the first polymer component which isprimarily responsible for permeability.

It is particularly important that the first and second polymercomponents be selected in combination for forming a thermoplasticcomposition having optical clarity and compatibility. Thermoplasticityis an essential feature of the composition of the present invention inorder to permit the use of low cost techniques such as molding orthermoforming. These low cost techniques, in turn, particularly adaptthe ocular lens composition of the present invention for use indisposable contact lenses.

The interpenetrating network of the contact lens composition of thepresent invention is formed by solution polymerization in order tofurther enhance optical clarity as discussed in greater detail below.More preferably, the interpenetrating network of the lens composition isformed by solution polymerization with a relatively high concentrationof a free radical initiator of greater than 0.9 molar percent ofmonomer, preferably at least about 1.0 molar percent of monomer and morepreferably at least about 1.2 molar percent of monomer.

Solution polymerization is classically defined as a reaction in whichthe reactants are dissolved in a suitable organic solvent, the solventserving as a vehicle in which the polymerization reaction takes place.The technique has the advantage of permitting easier removal of heatproduced by the reaction and, therefore, easier control of the reaction.Moreover, solution polymerization is more likely to follow knowntheoretical kinetic relations and therefore offers certain advantagessuch as the ability to be scaled up more readily. Finally, in theproduction of contact lenses, the polymer solution can be easilyfiltered and cast to further assure optical clarity and a fixedthickness for the lens blank used in the matched die molding which isthe next step of the lens manufacturing process.

The preceding definition of solution polymerization is taken from apublication by Stephen L. Rosen, entitled Fundamental Principles ofPolymeric Materials, pp. 179-181, John Wiley & Sons, New York, N.Y.

Within the solution polymerization of acrylic monomers, both diacylperoxides and azo compounds are frequently used as free-radicalinitiators. Examples of diacyl peroxides include benzoyl peroxide,4-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, isobutyroylperoxide, acetyl peroxide, propionyl peroxide, lauryol peroxide,decanoyl peroxide and diisopropylperoxydicarbonate. Azo compoundssuitable for these polymerization reactions are exemplified by2,2'-azobis(isobutyronitrile), 2,2'-(2-methylbutyronitrile),1,1'-azobis(cyclohexane-carbonitrile), and2,2'-azobis(2,4-dimethylvaleronitrile). Suitable monomers with whichthese initiators are used are disclosed elsewhere herein.

Benzoyl peroxide is one particularly representative example of a freeradical initiator for use in the present invention as indicated furtherbelow in the experimental section. As will be made apparent in theexperimental section, it is particularly contemplated that the initiatorbe present in the reaction in a concentration greater than 0.9 molarpercent of monomer, preferably more than 1.0 molar percent of monomerand more preferably greater than about 1.2 molar percent of monomer.These values were experimentally established particularly with benzoylperoxide as the initiator. However, similar concentrations are alsocontemplated for other free radical initiators such as those listedabove.

At the same time, thermoplastic compositions have other advantages inapplications contemplated by the present invention, such as the abilityto form different molded sections of the lenses to achieve differentcharacteristics using a thermoplastic lamination process to produce thefollowing types of lenses:

(a) A lens with a relatively rigid center and a relatively flexibleskirt formed by thermoplastically laminating a rigid central disc to asoft annular ring. Such a lens has superior qualities for masking severeastigmatism at low cost because the more rigid center provides theoptical quality required to correct the astigmatism and the moreflexible skirt provides the comfort and high oxygen permeability; and

(b) A cosmetic lens with the emulsion from a photograph of an actualiris thermoplastically laminated between two thin discs of material (aphototransfer) providing the most life-like cosmetic lens possible foruse with disfigured eyes or as a greatly-improved eye color change lens.

The method by which GP lens compositions are formed according to thepresent invention is broadly illustrated in FIG. 1 which is a flowdiagram illustrating the preferred use of first and second monomers forforming a first polymer component which is then combined with a secondpolymer component as discussed above to achieve various characteristicsin the resulting GP lens composition. Additional post-polymerizationtechniques are also set forth in the flow chart of the figure to furtherenhance characteristics of the finished GP contact lens composition. Asnoted above, the final step in the method or flow chart is the moldingor thermoforming of the IPN related first and second polymer componentsto produce the GP lens composition of the invention.

The GP lens composition and method of formation as discussed above arefurther exemplified by the following experimental material.

Experimental Section

The following examples are set forth for the purpose of furtherclarifying the content and scope of the present invention.

EXAMPLE 1

A polymerization tube was charged with 1.5 grams of a block co-polymerof poly(dimethylsiloxane) and poly(carbonate) based on bisphenol-A. (SeeHoward A. Vaughn, "The Synthesis and Properties of Alternating BlockPolymers of Dimethylsiloxane and Bisphenol-A Carbonate," in PolymerLetters, Vol. 7, pp. 569-572 (1969). (Also see U.S. Pat. No. 3,419,534issued Dec. 31, 1968 and U.S. Pat. No. 3,419,635 also issued Dec. 31,1968, both to Vaughn. Also, see D. G. LeGrand, "Mechanical and OpticalStudies of Poly(dimethylsiloxane) Bisphenol-A PolycarbonateCo-polymers", in Polymer Letters, Vol. 7, pp. 579-585 (1969). Thesereferences are incorporated herein to disclose the manner of forming theblock co-polymer employed in Example 1.

The polycarbonate comprises between about 40 to 45% by weight of theblock co-polymer and the polydimethylsiloxane comprises about 60 to 55%by weight of the block co-polymer. Dichloromethane was added topartially fill the tube and the block co-polymer was dissolved therein.

To the tube was added 0.5 ml of monomeric methyl methacrylate, without astabilizer, and 0.72 milligrams of benzoyl peroxide dissolved indichloromethane.

The polymerization tube was then filled with dichloromethane and tightlycapped. The tube was heated to 80 to 90 C. for 18 hours. The resultingsolution was a clear, very light straw-colored liquid.

The solution was cast on a glass plate and the dichloromethane allowedto evaporate in a stream of filtered air. A transparent film was formedon drying. The film was washed in heated distilled water and dried in aparticle free environment.

Small circular blanks were cut from the film and placed in a matched diemold formed to the contours of a contact lens. The mold was heated to atemperature of 100 to 150 C. and then slowly cooled to room temperature.A formed film was removed from the mold and edged.

The film in Example 1 comprised a contact lens according to the presentinvention and included various desired characteristics resulting fromthe interpenetrating network structure including the first and secondpolymer components referred to in Example 1.

EXAMPLE 1A

This example represents a range of compositions as variations ofExample 1. The purpose of this example is to demonstrate the breadthpossible for the ratios of monomers in the block copolymer and also toidentify a relatively broad range of monomers suitable for use therein.

Initially, Example 1 was specific to a polycarbonate comprising betweenabout 40 to 45% by weight of the block copolymer andpolydimethylsiloxane comprising about 60 to 55% by weight of the blockcopolymer. In this example, it is to be understood that substantiallybroader ranges are possible. Generally, it is contemplated that thesiloxane monomer may preferably comprise about 25 to 85% by weight ofthe block copolymer as noted for example in a paper by A. Barrie, M. J.L. Williams and H. G. Spencer, "Gas Transport in Heterogeneous PolymerBlends," Journal of Membrane Science, 21 (1984) 185-202, ElsevierScience Publishers B.V. Amsterdam. That reference is incorporatedtogether with the other references noted above for purposes of fullydisclosing possible compositions for use in the present invention. Atthe same time, the other monomer may comprise from about 75 to about 15%by weight of the block copolymer. Even more broadly, it is contemplatedthat the siloxane monomer may comprise from about 10 to about 90% byweight of the block copolymer, the balance being the other monomer.

As for possible identities of the first and second monomers in the blockcopolymer, the first monomer is preferably a siloxane compound with theother monomer being selected from a relatively broad range of compounds.Examples of monomers for the block compound are identified in a table onpages 393-394 of the Noshay reference noted above. That reference isalso incorporated herein. More specifically, the first monomer maycomprise methylphenylsiloxane (C block=dimethylsiloxane),dimethylsiloxane, siloxanes, phenylmethylsiloxane, aluminosiloxane. Theother monomer may at the same time comprise diphenylsiloxane,phenylmethylsiloxane, phenylsilsesquioxane,tetramethyl-p-silphynsylenesiloxane,tetramethyl-1,4-naphthalenesiloxane,tetramethyl-1,3-tetrafluorophenylenesiloxane, alkylene ethers,polysulfone, poly(phenylene oxide), isoprene, styrene, α-methylstyrene,α-methylstyrene-styrene, bisphenol A carbonate,9,9-Bis(4-hydroxyphenyl)fluorene carbonate, tetrabromobisphenol Acarbonate, 2,2,4,4-tetramethyl-1,3-cyclobutylene carbonate, bisphenol Aisophthalate, bisphenol A terephthalate, hexamethylene terephthalate,τ-benzyl L-glutamate, nylon 6, urethane, urea, imide. It is noted thatalthough the second monomer may be selected from a variety of compounds,the first monomer is preferably dimethylsiloxane.

Except for the ratios and specific identities of the monomers as setforth above, Example 1A is otherwise generally similar to Example 1. Itis to be noted that some variations may be necessary between thisexample and Example 1, for example, the selection of solvents. However,the selection of such solvents would be generally known to those skilledin the art.

Examples 1 and 1A, as well as the other examples set forth hereinbelow,demonstrate the unexpected novelty and utility of the lens compositionand method of the present invention to form lens compositions havingdesirable characteristics of flexibility, moldability and gaspermeability. These characteristics, particularly the level of gaspermeability, make the contact lens of the invention particularlysuitable for extended wear.

EXAMPLE 1B

This example is also a variation of Example 1. Duplicate polymerizationtubes were prepared as in Example 1 with the quantities of reactantsnoted in Table 1A below. As in Example 1, methylene chloride was thesolvent, the copolymer and the benzoyl peroxide initiator beingdissolved separately and then mixed with the methyl methacrylatemonomer.

                  TABLE 1a                                                        ______________________________________                                                                    BENZOYL CONC.                                     SAMPLE BLOCK      MMA       PEROXIDE                                                                              INITIATOR                                 DESIG- COPOLYMER  MONOMER   INITIATOR                                                                             AS MOLAR %                                NATION gms        millimoles                                                                              millimoles                                                                            OF MMA                                    ______________________________________                                        A      31.5       95        0.64    0.69                                      B      31.5       95        0.86    0.91                                      C      31.5       95        1.29    1.36                                      ______________________________________                                    

The tubes were heated to 90 degrees Celsius (90° C.) for 24 hours.Formulation A yielded cloudy solutions which cast to cloudy filmsunsuitable for optically clear contact lenses. One of the tubes informulation B was cloudy in solution; the other was clear. Films castfrom both tubes of formulation B were cloudy or possessed of a bluishhaze making them unsuitable for optically clear contact lenses. Bothtubes from formulation C were clear in solution and cast to filmssuitable for optically clear lenses.

The series of formulations in Table 1A demonstrate the unexpectedsensitivity of these formulations to initiator concentration. Generally,in the art of methylmethacrylate polymerization, particularly, benzoylperoxide levels of 0.1% or lower are suitable for successfulpolymerizations. However, it is believed that in this case, the higherlevels of benzoyl peroxide have the effect of minimizing the chainlength of the poly(methyl methacrylate). Shorter PMMA chains arebelieved to yield compatible IPNs which do not possess microphaseseparation. As noted above, incompatibility results in cloudy filmswhich are unsuitable for optically clear contact lenses.

Although Example 1B was carried out with benzoyl peroxide as the freeradical initiator, it is believed that the general concentration levelsindicated in Example 1B also apply to the other free radical initiatorslisted above. Accordingly, Example 1B indicates the desirability for afree radical initiator in a solution polymerization reaction accordingto the present invention of greater than about 0.9 molar percent ofmonomer, preferably at least about 1.0 molar percent of monomer and morepreferably at least about 1.2 molar percent of monomer.

Generally, although the concentration of 0.91% benzoyl peroxide wasmarginal and possibly not acceptable for most lens applications, takenin the context of Example 1B and Table 1A, it is believed to establish ageneral minimum concentration of initiator according to the invention.Similarly, an initiator concentration of at least about 1.0 molarpercent of monomer is believed to be sufficiently higher thanformulation B of Table 1A to provide acceptable characteristics for mostlens applications. Certainly the higher minimum concentration of about1.2 molar percent of monomer is believed to provide good characteristicsin contact lens applications. That minimum value is close to theinitiator concentration of 1.36 molar percent of monomer in formulationC which was found to provide excellent characteristics, particularly interms of optical clarity. Furthermore, it is believed that an increaseof initiator concentration substantially above the concentrationsdiscussed above and set forth in Example 1B would not result in anyfurther substantial advantage for the resulting composition. Morespecifically, it is anticipated that little additional benefit would beachieved from initiator concentrations of about 1.5 molar percent ofmonomer or greater.

The values discussed above and the compositions set forth in Example 1Bare believed to demonstrate an unexpected sensitivity of the lensformulations to initiator concentration and to add to patentable noveltyof the invention. In this regard, the prior art regarding MMApolymerization has generally taught the use of benzoyl peroxide levelsof about 0.1 molar percent of monomer or lower as an initiator forsuccessful polymerization. Accordingly, the present inventionunexpectedly teaches the use of initiator levels of about a full orderof magnitude greater than anticipated in the prior art.

It is also noted again that the concentrations indicated in Example 1Band Table 1A are also believed representative for other monomers andfree radical initiators as described and listed elsewhere herein.

It is also particularly important to note that the minimum initiatorconcentrations discussed above are preferably contemplated in a solutionpolymerization reaction as described above. Example 1 and other examplesherein are representative of such solution polymerization reactionswhich achieve the desired characteristics of the present invention.Example 1B thus combines both solution polymerization and a minimumconcentration of free radical initiator to provide a particularlydesired combination of features according to the present invention,particularly optical clarity in a gas permeable lens preferably suitablefor extended wear.

EXAMPLE 2

This example represents a series of compositions which are alsographically illustrated in FIG. 2. Briefly, the steps of Example 1 wererepeated with the percentage of the second polymer component methyl(methacrylate) (MMA) being present in percentages of the entirecomposition ranging from about 0 to about 25. Table 1B represents oxygenpermeability Dk (x10⁻¹¹) in units of (cm² /sec)·(m10₂ /ml×mmHg)! foreach of the different compositions. The various concentrations of thesecond polymer component and corresponding permeabilities are alsorepresented in tabular form below:

                  TABLE 1B                                                        ______________________________________                                        Oxygen     Second Polymer Component                                           Permeability                                                                             (MMA) Concentration                                                Dk         (Percentage of entire composition)                                 (x10.sup.-11)                                                                            by weight                                                          ______________________________________                                        180        0.0                                                                141        5.0                                                                105        9.0                                                                 62        22.0                                                                49        25.0                                                               ______________________________________                                    

The formed films produced for each of the compositions set forth abovealso provided an optically clear/compatible composition suitable for usein contact lens compositions.

In addition, the multiple compositions set forth in Example 2 representa preferred manner of varying the amount of one component in the lenscomposition for sequentially adjusting a preferred characteristic suchas oxygen permeability. It is further to be noted that the compositioncould similarly be varied for adjusting other desired characteristicssuch as rigidity/flexibility or structural stability, for example.

The contact lens compositions of the present invention are described forexample in Example 2 and elsewhere herein with particular reference tooxygen permeability. In this regard, oxygen permeability is consideredto be a particularly important indicator because it is an absolute valuefor the composition without reference to thickness of the lens or otherdimensional factors. By contrast, equivalent oxygen percent (EOP) is acorresponding value discussed in connection with contact lenses, forexample, as discussed by John K. Fitzgerald in a paper entitled"Understanding Permeability and Wettability", in The Contact LensJournal.

Although specific EOP values have not been measured for the compositionsof the present invention, it is clearly anticipated that thecompositions contemplated for the invention and specifically disclosedin the experimental section will have EOP values for the lenses formedaccording to the present invention clearly exceeding a minimum value ofabout 10% which is considered to be essential or at least necessary forsatisfactory extended wear contact lenses by Fitzgerald and others.

The concept of EOP as a method of describing oxygen permeability ofcontact lenses and the like was also described in an article by LoshaekS., Hill R. M., "Oxygen Permeability Measurements: Correlation BetweenLiving-Eye and Electrode Chamber Measurements", International ContactLens Clinic, (Nov.-Dec. 1977, pp. 26-29). The articles by Hill andFitzgerald are incorporated by reference as though set forth herein intheir entirety.

EXAMPLE 3

The steps of Example 1 were again repeated. However, in addition to themonomeric methyl methacrylate, a range of 0.5 to 2.5% by weight (totalsolids) of N-vinyl-2-pyrolidone was added to the solution. The resultingfilms within the above range exhibited enhanced surface wettingcharacteristics as demonstrated by examination of the contact angle ofdistilled water on the polymer film surface.

EXAMPLE 4

The steps of Example 1 were again repeated. However, in addition tomonomeric methyl methacrylate, 0.5 grams of acrylamide and 0.2 grams of2, hydroxyethyl methacrylate were added to the polymerization mixture inseparate compositions.

Cast films formed from both of the compositions in Example 4 showedwetting angles with distilled water, relative magnitude being indicatedas: PMMA alone>2,hydroxyethyl methacrylate addition>acrylamide addition.

EXAMPLE 5

The steps of Example 1 were again followed. However, in place of themethyl methacrylate monomer as the second polymer component, monomericstyrene was added to the PDMS-b-PC! block co-polymer solution.

Different compositions were formed with the monomeric styrene varyingfrom about 1 to at least about 5% of the composition by weight.

Films formed from the above compositions each illustrated opticalclarity and accordingly polymer compatibility in accordance with thepresent invention.

Steps of the preceding examples may also be carried out employingdifferent polymers, for example those listed above while realizinggenerally similar advantages of the invention.

EXAMPLE 6

The steps of Examples 1 and 2 were again followed. The thermally formedlenses produced in this example were treated in a chamber designed tocreate different plasma surface treatment environments. The lenstreatment consisted of three process steps, each using a primary gasplasma created at a frequency of 13.56 MHz. The first process involvedexposing the lens to an oxygen plasma, the second was a plasma createdwith methane, and the third step repeated exposure to an oxygen plasma.The lenses so treated exhibited enhanced surface wettability asdemonstrated by examination of the contact angle of distilled water onthe lens material and tear break-up time experiments on the lensesthemselves.

The previous examples were early examples which demonstrated a number ofgeneral characteristics of the scope of the invention.

The following examples included clinical evaluations demonstrating morespecifically how the choice of polymers and/or monomers and theproportions thereof can be selected to achieve a certain type of contactlens with certain desired characteristics.

EXAMPLE 7

The objective of this example was to obtain a non-water-based, highlyflexible "soft" lens. That is, a lens that has the immediate comfort andfit characteristics of a soft water-based hydrogel lens, but, because ofthe absence of water, does not suffer from dehydration causing lesssharp vision and eye irritation. In addition, another objective was toavoid the potential for microorganism infection caused by thewater-based nature of the soft hydrogel lenses.

The steps of Example 1 were followed with the high rigidity monomericmethyl methacrylate (see Table 2) being replaced by butyl acrylate,yielding a polymer tending to be much more flexible than polymethylmethacrylate. Small circular blanks were cut from the resulting film andplaced in a thermal pressure molding apparatus with molds designed for aspecific subjects' prescription at a 14 mm lens diameter, the standardhydrogel lens diameter. The temperature was increased to 165° C. underpressure and slowly cooled to room temperature. The resulting contactlens was 14 mm in diameter with a 0.2 mm center thickness. Thereplacement of the methyl methacrylate with butyl acrylate resulted in alens of generally the same gas permeability but one of much greaterflexibility (Table 2 indicates a factor of eight increase inflexibility) which had a feel similar to the feel and comfort of a softhydrogel lens. Upon undergoing the plasma surface treatment described inExample 6, the lens was clinically tested in the subject's eye. Theresults indicated a non water-based lens that had the initial comfort ofa hydrogel soft lens and the superior visual acuity characteristics ofan RGP lens.

The flexural modulus values discussed in Example 7 with reference toTable 2 are capable of correlation with the ratio of the first andsecond polymer components as discussed typically in Example 2. Sourcesof the data in Table 2 are indicated by parenthetical numberscorresponding to the footnotes following Table 2.

Referring to both of these examples in combination, the presentinvention generally contemplates a preferred range for the secondpolymer component of about 2-30% by weight. That range is selectedprimarily for purposes of maintaining desired gas permeability withinthe resulting GP lens.

                                      TABLE 2                                     __________________________________________________________________________    APPROXIMATE FLEXURAL MODULUS OF KEY MATERIAL                                  COMPOSITIONS REFERRED TO IN EXAMPLES                                                                 FLEXURAL MODULUS                                       MATERIAL               dynes/cm.sup.2                                                                      psi  Ratio                                       __________________________________________________________________________    MOST  Polymethyl Methacrylate (100%)                                                               (1)                                                                             .sup. 2.8 × 10.sup.10                                                         400,000                                                                            1.0                                         RIGID Polydimethylsiloxane-                                                                        (2)                                                                             2.6 × 10.sup.0                                                                370,000                                                                            9.3 × 1.sup.-1                              polycarbonate(2) (10%)-                                                       i-polymethyl methacrylate (90%)                                               Polydimethylsiloxane-                                                                        (3)                                                                             2.8 × 10.sup.9                                                                40,000                                                                             1.0 × 10.sup.-1                             polycarbonate (75%)-i-                                                        polymethyl methacrylate (25%)                                                 Polydimethylsiloxane-                                                                        (3)                                                                             2.5 × 10.sup.9                                                                36,000                                                                               9 × 10.sup.-2                             polycarbonate (990%)-i-                                                       polymethyl methacrylate (10%)                                                 Polydimethylsiloxane-                                                                        (3)                                                                             3.5 × 10.sup.8                                                                 5,000                                                                             1.3 × 10.sup.-2                             polycarbonate (75%)-i-                                                        butyl acrylate (25%)                                                    MOST  The Cornea of the Eye                                                                            1 × 10.sup.8                                                                 1,500                                                                             3.6 × 10.sup.-3                       FLEXIBLE                                                                            Typical Hydrogel (PolyHEMA)                                                                  (4)                                                                               5 × 10.sup.7                                                                  750                                                                              1.8 × 10.sup.-3                       __________________________________________________________________________     1. Modern Plastics Encyclopedia, McGraw Hill 1984-1985.                       2. Arkles U.S. Pat. No. 4,478,981 issued October 23, 1984.                    3. Experimentally determined values.                                          4. Contact Lenses, Vol. 2, Chap. 13, edited by J. Stone and A. J.             Phillips, Buttersworths, 1981.                                           

Referring also to Example 7, it may be seen that the flexural modulus ofthe lens generally correlates with the ratio set forth above but alsowith the specific identity of the second polymer component. Generally, arange of flexural modulus values for the present invention encompassesabout 2,000-50,000 psi, more preferably about 5,000-40,000 psi and mostpreferably about 20,000-40,000 psi.

These flexural modulus values are also selected based on the possibilityof substitution particularly for the second polymer component. Forexample, the flexural modulus for the resulting lens may be variedeither by changing the ratio of the first and second polymer componentsor by varying the second polymer component itself. For example, asubstantially lower flexural modulus would result by substituting apolymer such as butyl acrylate in place of methyl methylacrylate.

The inverse relationship between permeability and stiffness in contactlenses is well established. See for example FIGS. 3 and 4 in a paper byIrving Fatt, "Performance of Gas Permeable Hard Lenses on the Eye",Transactions of the British Contact Lens Association, 1986, pp. 32-37.

EXAMPLE 8

The objective of this example was to produce a superior 10-11 mmdiameter RGP type lens with very high oxygen permeability. The steps ofExample 1 were followed with the proportion of monomeric methylmethacrylate reduced to approximately 10% by weight of the totalcomposition. Small circular blanks were cut from the resulting film andplaced in a thermal pressure molding apparatus with molds designed for aspecific subjects prescription in a 10.5 mm diameter with typical RGPlens design characteristics. The temperature was increased toapproximately 165° C. under pressure and slowly cooled to roomtemperature. The resulting contact lens was 10.5 mm in diameter with a0.15 mm center thickness. The lens was then clinically tested in thesubjects eye. It was found to be more comfortable than a typical hardRGP lens because of its increased flexibility (see FIG. 4) andtranslated well under blinking on the eye, because the 10% MMAconcentration added sufficient rigidity such that blinking did notoverly deform the lens. The relative permeability, Dk, as noted inExample 2, was approximately 100, which is generally considered a veryhigh permeability. The wettability of the lens under clinical evaluationwas determined to be adequate without any additional surface treatment.

EXAMPLE 9

The objective of this example was to produce a superior scleral lenswhich is often used on subjects having pathological eye conditionscaused by poor corneal grafts or keratoconus. A typical scleral lens is16-22 mm in diameter whose optic portion of approximately 13-14 mmdiameter vaults over the cornea such that it does not contact it andonly makes contact on the outer sclera.

The steps of Example 1 were followed with the methyl methacrylatecomposition chosen to be approximately 25% of the total. Circular blankswere again placed in the thermal pressure molding apparatus and molded,as in Examples 7 and 8. In this case the mold was designed to produce an18 mm diameter lens with a 13.5 mm optical vaulted section. The lens wasclinically evaluated on a subjects eye and found to be more comfortablethan a standard scleral lens, which is typically machined frompoly(methyl methacrylate) (PMMA) or hard machinable RGP material. Thesubject's visual acuity was increased from approximately 200/20 toapproximately 30/20 and the resulting lens had a relative oxygenpermeability of approximately Dk=50, which is greatly superior to PMMA.In this example, the relatively superior comfort was due to the greaterflexibility of the silicone polycarbonate. However, the 25% MMA providedsufficient rigidity for the vaulted section to prevent it from deformingunder blinking. Wettability was considered adequate but was subsequentlygreatly enhanced by surface treatment, as indicated in Example 6.

EXAMPLE 10

The objective of this example was to produce a contact lens withimproved characteristics for subjects with a high degree of astigmatism.These characteristics include comfort comparable to a hydrogel lens,high oxygen permeability, and, most importantly, sharp, clear vision. Astandard soft hydrogel lens cannot readily correct severe astigmatismbecause the astigmatism is caused by a "football"-shaped cornea. A softhydrogel lens is so flexible that it drapes over the cornea and,therefore, does not provide adequate vision correction. RGP lenses cancorrect for astigmatism but suffer from inadequate initial comfort andhigh cost, as stated earlier. In this example, the thermoplastic natureof the materials was used to laminate a partially rigid center to a veryflexible, highly permeable skirt. The steps of Example 7 were followedwith a butyl acrylate concentration of approximately 20-25% by weight.Small circular blanks were cut from the film. Then, the steps of Example1 were followed with a methyl methacrylate composition of approximately25% by weight. Referring to FIGS. 4 and 5, circular blanks ofapproximately two-thirds the diameter of the first circular blanks werecut from this film to form blank components such as that indicated at10. A circular section of approximately one-half the diameter wasremoved from the larger circular blank with a punch and discardedleaving an annular blank 12. The remaining blanks 10 and 12 were placedin the thermal pressure molding apparatus, as described in the earlierexamples (not shown), and were thermoplastically laminated into a lens14. The resulting lens 14 was 14 mm in diameter with an approximately9.5 mm center section (formed by the blank component 10) with a smoothclear transition 16 between the two sections.

Upon clinical evaluation it was found that the center section wassufficiently rigid to mask severe astigmatism yet not too rigid toimpair comfort, while the outer flexible skirt provided enhanced comfortand relatively high oxygen permeability.

EXAMPLE 11

The objective of this example was to produce a superior lens thatbecomes a cosmetic cover for a disfigured eye or an extremely life-likeiris color-change lens. In this example, the steps of Example 1 werefollowed. Small circular blanks were cut from the film, which, in thisexample, was purposely somewhat thinner than previous films. Twocircular blanks 22 and 24 were selected for the molding/laminationprocess to follow. Sandwiched between the two blanks in the mold was anemulsion film 26 of a photograph of the iris of a preselected eye withthe pupil removed. The same thermal pressure molding apparatus wasutilized as in previous examples to encapsulate the film 26 between theblanks 22 and 24 and form a resultant lens 28 having similar comfort,oxygen permeability and other features previously described but also hadan accurately realistic iris for cosmetic or color-change purposes. Theemulsion could of course be replaced by other films having a desiredimage.

The lens compositions demonstrated by the preceding examples provide anumber of advantages for lenses formed according to the invention.

Because of the monomer selection for the invention as defined above inthe first and second monomer components of the second polymer component,it is possible to achieve a degree of flexibility or softness and, morespecifically, a variable range of flexibility (as preferably measured bya lowering of the flexural modulus, see FIG. 4) to enhance the inherentcomfort of the resulting lens. Lens flexibility is known to be a majorfactor in patient acceptance of contact lenses of the type contemplatedby the present invention. Furthermore, flexibility of the degreecontemplated by the present invention has generally not been possible inthe prior art in practical gas permeable (non-hydrogel) lenses,specifically with the lens compositions contemplated by U.S. Pat. No.4,478,981 issued Oct. 23, 1984 to Arkles or U.S. Pat. No. 4,550,139issued Oct. 29, 1985 also to Arkles.

The first noted Arkles patent disclosed a lens system in which a smallproportion of a block copolymer was added to a relatively largeproportion of poly(methyl methacrylate).

It is to be noted that the ratios between the first and second polymercomponents of the present invention are in contradistinction to theratios disclosed in the Arkles patent and, as shown in FIG. 4, lenses ofthe present invention are approximately 9 to 75 times more flexible.

It is further noted that the small proportions of the block co-polymeremployed in the compositions of the above noted patent, with aproportionally smaller silicone component, create a lens compositionwhich, in fact, is not only inferior for the types of applications inthis invention, but is inappropriate for practical long wearing lenses.Furthermore, the low oxygen permeability levels exhibited for suchmaterial are far below those practical for extended wear according tothe present invention.

Continuing with reference to the Arkles patents noted above, it isfurther emphasized that the monomers employed in the first and secondpolymer components of the present invention are particularly selected inorder to contribute to the flexibility of the resulting lens aspreviously discussed.

It is again emphasized that key features of the lens compositionsaccording to the present invention are transparency and clarity withinthe resulting lens. This requires that the components of the lenscomposition be completely compatible. Otherwise small phase boundariesmay exist within the resulting lens which will create cloudy conditions.For example, the Arkles patent noted above employed both melt blendingand in situ polymerization in order to achieve compatibility between thedifferent components of the lens composition. However, it is believedthat these techniques from the above reference result in some loss ofclarity and also in the introduction of crosslinking into the polymerstructure which has the undesirable effect of minimizing oxygenpermeability.

By contrast, the selection of monomers, the ratios of first and secondpolymer components, the amount of initiator and the methods disclosedfor combining these components into the lens composition for the presentinvention result in superior optical clarity for the lens and maximizesoxygen permeability therein.

The compositions of the present invention are also disclosed in thepreceding examples and elsewhere as being suitable for formation of thelens by thermoplastic molding. This offers a novel degree of flexibilityin shaping and contouring the lens formed according to the presentinvention. As noted above, the combination of relatively rigid andrelatively flexible thermoplastic materials made possible by the moldingtechniques contemplated for the present invention permit the creation oflens designs, for example, possessing more rigid central portions inwhich exact optical corrections can be molded with a more flexible andmore comfortable and gas permeable peripheral annulus for the lens.

Furthermore, the materials of the lenses according to the presentinvention can be molded to, for example, readily vault over portions ofthe eye where pathological conditions require avoiding direct contactwith portions of the cornea or other eye portions. Such molded vaultingdesigns also provide the opportunity to mask highly astigmatic eyeconditions.

Yet another advantage of the present invention is the possibility ofemploying thermoplastic molding to form or fabricate color changingcontact lenses. In this regard, the prior art has disclosed contactlenses which are merely printed or in which colorants are surface orvolume embedded. With the present invention, it is possible to duplicateexactly the appearance of an existing eye by photographing it and thencapturing the actual photoemulsion containing the image between two thinmolded layers of thermoplastic material according to the presentinvention. Lenses created using photographed images in this manner thusappear more natural than those made using other techniques.

As noted above, certain characteristics of lenses formed according tothe present invention can be further enhanced. For example, wettabilityof the lens may be enhanced by plasma treatment as described above inExample 6. Although the addition of hydrophilic monomers described inExamples 4 and 5 offer one approach to lens wettability, it has beenfound that when certain plasma treatment methods are used, wettabilityof the lens can be substantially enhanced.

Tear break-up time is one criterion for practical lens wettability. Thelonger the tear break-up time, the more wettable, i.e. desirable is thelens. In this test the lens is placed on the subject eye in its normalposition. A close-up image of the eye is then videotaped with thepatient being directed to blink to wet the lens surface and then torefrain from blinking for as long as possible. The time between theblink and the break-up of the continuous tear fluid film over the lenssurface is then noted. Typical tear break-up values for existing RGPcontact lenses are in the range of 8 to 20 seconds. Lenses made from thematerials and polymer preparation techniques of the present inventionhave extended tear break-up time(s) ranging from 45 seconds to in excessof 60 seconds.

Accordingly, there has been disclosed above a variety of GP ocular lenscompositions and polymer preparation techniques for achieving greatlyenhanced characteristics in the lens composition. Additionalmodifications and variations will be apparent from the precedingdescription and examples, as well as the following claims which are alsoset forth by way of example. Accordingly, the scope of the invention isdefined only by the following appended claims.

What is claimed is:
 1. A method for producing a gas permeable ocularlens, comprising:(a) preparing a solution containing(1) a first polymercomponent comprising about 70-98% by weight of the composition of thelens that is a block copolymer comprising first and second blocks, thefirst block being selected from silicones and fluorocarbon polymers andthe second block being selected from polycarbonates, polysulfones, andpolystyrene; and (2) a monomer polymerizable to form a second polymercomponent comprising about 30-2% by weight of the composition of thelens, the monomer being selected from the group consisting of acrylates,methacrylates, pyrrolidones, styrene, amides, acrylamides, carbonates,vinyls, acrylonitrile, nitriles, sulfones, siloxanes, glycols, ethers,and combinations thereof; in a solvent effective for the first polymercomponent and the monomer; (b) polymerizing the monomer in the absenceof a cross-linking agent to form the second polymer component so thatthe first and second polymer components form an interpenetrating polymernetwork within the solution; (c) removing the solvent from the solutionto leave a solid thermoformable gas permeable ocular lens composition;and (d) thermoforming the composition into a gas permeable ocular lens.2. The method of claim 1 where the first polymer component is asilicone-polycarbonate block copolymer.
 3. The method of claim 2 wherethe first polymer component is a polydimethylsiloxane-poly(bisphenol Acarbonate) block copolymer.
 4. The method of claim 3 where the monomeris an acrylate or methacrylate.
 5. The method of claim 4 where themonomer is methyl methacrylate.
 6. The method of claim 1 where thepolymerizing step (b) is carried out in the presence of a free radicalinitiator at a concentration of at least 0.9 molar percent of themonomer.
 7. The method of claim 6 where the concentration of the freeradical initiator is at least 1.0 molar percent of the monomer.
 8. Themethod of claim 7 where the concentration of the free radical initiatoris at least 1.2 molar percent of the monomer.
 9. The method of claim 1where the solvent removing step (c) comprises casting the dissolvedinterpenetrating polymer network into sheet form and evaporating thesolvent to leave a solid sheet of the thermoformable gas permeableocular lens composition.
 10. The method of claim 9 where thethermoforming step (d) comprises forming a blank in the shape of acontact lens from the sheet of the thermoformable gas permeable ocularlens composition and thermoforming the blank into a gas permeable ocularlens.
 11. A method for producing a thermoformable gas permeable ocularlens, comprising:(a) preparing a solution containing from 70-98% byweight of the composition of the lens of apolydimethylsiloxane-poly(bisphenol A carbonate) block copolymer andfrom 30-2% by weight of the composition of the lens of methylmethacrylate in a solvent effective for the block copolymer and themethyl methacrylate; (b) polymerizing the methyl methacrylate in theabsence of a cross-linking agent and in the presence of at least 0.9% ofa free radical initiator to form poly(methyl methacrylate) so that thepolydimethylsiloxane-poly(bisphenol A carbonate) block copolymer and thepoly(methyl methacrylate) form an interpenetrating polymer networkwithin the solution; (c) removing the solvent from the solution to leavea solid thermoformable gas permeable ocular lens composition; and (d)thermoforming the composition into a gas permeable ocular lens.
 12. Themethod of claim 11 where the solvent removing step (c) comprises castingthe dissolved interpenetrating polymer network into sheet form andevaporating the solvent to leave a solid sheet of the thermoformable gaspermeable ocular lens composition.
 13. The method of claim 12 where thethermoforming step (d) comprises forming a blank in the shape of acontact lens from the sheet of the thermoformable gas permeable ocularlens composition and thermoforming the blank into a gas permeable ocularlens.
 14. A thermoformable gas permeable ocular lens comprising aninterpenetrating network of a first polymer component comprising about70-98% by weight of the composition of the lens that is a blockcopolymer comprising first and second blocks, the first block beingselected from silicones and fluorocarbon polymers and the second blockbeing selected from polycarbonates, polysulfones, and polystyrene, and asecond polymer component comprising about 30-2% by weight of thecomposition of the lens that is a polymer of a monomer selected fromacrylates, methacrylates, pyrrolidones, styrene, amides, acrylamides,carbonates, vinyls, acrylonitrile, nitriles, sulfones, siloxanes,glycols, ethers, and combinations thereof, the lens being formed by thesolution polymerization of the monomer forming the second polymercomponent in the presence of the first polymer component and the absenceof a cross-linking agent, removal of the solvent to leave a solidcomposition, and thermoforming of the resulting solid composition into agas permeable ocular lens.
 15. The lens of claim 14 where the firstpolymer component is a silicone-polycarbonate block copolymer.
 16. Thelens of claim 15 where the first polymer component is apolydimethylsiloxane-poly(bisphenol A carbonate) block copolymer. 17.The lens of claim 16 where the monomer is an acrylate or methacrylate.18. The lens of claim 17 where the monomer is methyl methacrylate. 19.The lens of claim 14 having a flexural modulus in the range of about2,000-50,000 psi.
 20. The lens of claim 19 having a flexural modulus inthe range of about 5,000-40,000 psi.
 21. The lens of claim 20 having aflexural modulus in the range of about 20,000-40,000 psi.
 22. A gaspermeable ocular lens, comprising an interpenetrating network of from70-98% by weight of the composition of the lens of apolydimethylsiloxane-poly(bisphenol A carbonate) block copolymer andfrom 30-2% by weight of the composition of the lens of poly(methylmethacrylate), the lens being formed by the solution polymerization ofmethyl methacrylate in the presence of thepolydimethylsiloxane-poly(bisphenol A carbonate) and the absence of across-linking agent, removal of the solvent to leave a solidcomposition, and thermoforming of the resulting solid composition into agas permeable ocular lens.
 23. The lens of claim 22 having a flexuralmodulus in the range of about 2,000-50,000 psi.
 24. The lens of claim 23having a flexural modulus in the range of about 5,000-40,000 psi. 25.The lens of claim 24 having a flexural modulus in the range of about20,000-40,000 psi.